The solution casting process of thin polymer films (also known as tape casting or band casting in the industry) involves spreading of a solution by a slot die, doctor blade or a reverse roll onto a carrier followed by subsequent removal of the solvent by the application of heat. Films ranging from several hundreds of microns thick to a couple of microns can be produced with extreme uniformity. Solution casting processes offer advantages for materials that cannot be melt processed or exhibit melt instabilities at small thickness ranges. Commercial solution casting machines have been manufactured for over five decades and come in a wide variety of designs. Commercial solution casting machines typically include a solid casting surface, a drying chamber with a built in means of controlling the airflow over the cast solution, an adjustable speed carrier drive control, an air heater to control the temperature of the filtered feed air to the drying chamber and under-bed heaters to set-up the desired temperature profile in the machine. The carrier is usually a rotating endless stainless steel belt, although other common polymeric or coated paper carriers are also found in industrial applications. This endless steel belt may also include under-bed heaters to conductively heat the cast medium from below. By the combined effect of air heating from above and conductive heating from below the cast fluid or partially fluid medium, the solidification through the removal of solvent and/or polymerization can be affected. Multiple carriers in a single solution casting machine are also possible.
The technique of electrospinning, also known within the fiber forming industry as electrostatic spinning, of liquids and/or solutions capable of forming fibers, is well known and has been described in a number of patents as well as in the general literature. The process of electrospinning generally involves the creation of an electrical field at the surface of a liquid. The resulting electrical forces create a jet of liquid which carries an electrical charge. These electrically charged jets of liquid may be attracted to a body or other object at a suitable electrical potential. As the liquid jet is forced farther and farther toward the object, it elongates. As it travels away from the liquid reservoir, it steadily dries and hardens, thereby forming a fiber. The drying and hardening of the liquid jet into a fiber may be caused by cooling of the liquid (i.e., where the liquid is normally a solid at room temperature); evaporation of a solvent (e.g., by dehydration); physically induced hardening; or by a curing mechanism (chemically induced hardening). The fibers produced by electrospinning techniques are collected on a suitably located charged receiver and subsequently removed from the receiver as needed.
Fibers produced by the electrospinning process have been used in a wide variety of applications and are known from, for example, U.S. Pat. Nos. 4,043,331 and 4,878,908, to be particularly useful in forming non-woven mats suitable for use in wound dressings. Other medical applications include drug delivery (see, e.g., U.S. Published Patent Application No. 2003/0195611), medical facemasks (see, e.g., WO 01/26610), bandages and sutures that minimize infection rate, blood loss and ultimately dissolve into body. Nanofibers also have promising applications in the area of filtration due to their smaller microporous structure with higher surface area. Electrospun nanofibers are ideal for filtering submicron particles from air or water. They improve filter life and have more contaminant holding capacity.